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What is a Heat Pump? And how do they work?

Recently, heat pumps have received some attention as we look for more sustainable living methods. This article answers two important questions: What is a heat pump, and how does it work?

To start, a heat pump is an HVAC system capable of both heating and cooling buildings. They are regarded as being incredibly energy-efficient and cost-effective over the long term. A heat pump system can be confusing if you don't already have one. Read on to learn more.

What is a heat pump?

heat pump
Photo by Arnt Brandseth on Wikimedia Commons licensed under CC BY-SA 4.0 (Cropped from original).

A heat pump is a heating system that can also serve as a cooling system. It's like a heater and air conditioner in one appliance. 

Heat pump systems typically use electricity to transfer heat energy to where you need it. During the heating season, a heat pump transfers heat from an outdoor source into your house. In the cooling season, it will pull heat out of your house. 

Heat pumps not only provide heat and cold air, they can also be used to supply hot water for households. The best thing about heat pumps is that they use little energy to do a lot of work. So, consider adding this to your sustainable lifestyle!

How does a heat pump work?

A heat pump collects heat from the outside air, ground, and water and concentrates it inside. It can also be reversed to collect and transfer heat from inside buildings to the outdoors. 

Heat energy naturally wants to move to lower-pressure environments (areas with lower temperatures). The heat pump encourages this natural transfer in a way that can either warm or cool your house. Heat pumps (not hybrids) do not generate heat. They are only capable of transferring heat.

Here's a quick summary of how a heat pump cool and heat your home;

  • A heat exchanger extracts heat from the source and brings it into the heat pump. 
  • The warmth passes over the refrigerant–a substance that absorbs and rejects heat–turning it into gas. Then, a compressor pressurizes the gas, raising its temperature. 
  • The heated gas goes through another heat exchanger, which transfers the warmth to a heat sink. The sink could be your home heating system or the outdoors if cooling mode is on.

A reversing valve is what differentiates a heat pump from an air conditioner. The reversing valve is the mechanism that allows a heat pump to reverse the flow of refrigerant. It makes it possible for the heat pump to switch between cooling or heating mode. 

Types of heat pumps 

There are 3 types of heat pumps according to their heat source: air source, water source, and ground source. 

Air source heat pumps

air source heat pump
Photo by 51% Studios Architecture on Flickr licensed under CC BY-SA 2.0 (Cropped from original).

The air source heat pump is the most common type. It moves heat energy between indoor and outdoor air. The two types of air-source heat pumps are air-to-air heat pumps and air-to-water heat pumps. An air source heat pump can be ducted or ductless.

The air handler unit (indoor unit) and outdoor unit of an air-to-air heat pump each have one fan and refrigerator coils. The fans move air in and out of the pump. The coils interchangeably act as evaporators or condensers, depending on whether the pump is in cooling or heating mode.

Reverse cycle chiller 

The reverse cycle chiller (RCC) heat pump works by transferring heat energy between an insulated water tank and a house. The RCC pumps heated or cooled water through ducts to designated zones. It works with an air outlet or a radiant floor heating system to heat up or cool down a house. An RCC can also connect to the household water supply system to provide heated water. 

In heating mode, the RCC system uses hot water from the tank to defrost its coils. This eliminates the need for the backup coils that most heat pumps require, so the RCC remains efficient in cold temperatures, even below zero degrees Celsius.

Ground source heat pumps 

Ground source heat pumps, also called geothermal heat pumps, transfer heat energy between your house and the ground or a water body outside. The water body can be a well or an artificial lake.

A ground source heat pump extracts heat using buried pipes filled with water and antifreeze. Geothermal heat pumps can be connected to underfloor heating systems and radiators.

A ground source heat pump will fit in most houses if there's enough space outside. This kind of heat pump isn't cheap to install, but it has impressively low running costs due to the constant temperature of the deep soil or groundwater.

Absorption heat pumps

absorption heat pump
Photo by Reinraum on Wikimedia Commons (Public Domain).

Absorption heat pumps are more complex than regular heat pumps. They do not use electricity but are powered using natural gas, geothermal-heated water, solar power, or propane. Absorption heat pumps are also called gas-fired heat pumps because natural gas is their most common heat source.

The main difference between an absorption heat pump and a standard one is that the former operates by absorbing ammonia. The ammonia is the refrigerant.

Absorption heat pumps are usually used for industrial applications but can be retrofitted for households. These heat pumps work perfectly for off-grid houses without electricity. It's more energy efficient than an open fireplace and supplies different degrees of warmth to other rooms. 

Hybrid heat pumps

A hybrid heat pump combines with a traditional heating system. An example is integrating a gas furnace or a boiler with air source or ground source pumps. It's referred to as a dual-fuel system. The hybrid system can not only provide heat but can also be used in cooling mode. 

The hybrid heating system allows your house to stay warm when it's too cold for the heat pump to provide optimal warmth. It can also save energy by monitoring the temperature outside and automatically choosing the most efficient energy source.

Hybrid heat pumps reduce electricity waste. However, the real savings would depend on the environmental costs of fuel vs electricity and how much of the better option it consumes.

Advantages of heat pump system

heat pump system
Photo by Ra Boe on Wikimedia Commons licensed under CC BY-SA 3.0 (Cropped from original).

Using heat pumps for home heating has both economic and environmental benefits. Let's look at some of the benefits in detail.

Saving money 

There's no need to install separate systems for cooling and heating, as heat pumps can do both, providing significant cost savings. Although heat pumps still cost quite a bit to set up, the overall cost is determined by the type of heat pump you want. For example, a ground-source heat pump is more expensive than an air-source heat pump. 

Heat pumps can also help you reduce your energy bills by as much as 1200 USD . The energy they consume is only a fraction of what they produce. That means more heating or cooling for less money.

Another way heat pumps can put back some money into your pocket is through tax credits. The Inflation Reduction Act (IRA) provides tax incentives for homeowners to replace their existing heating and cooling systems with more energy-efficient alternatives in the United States. 

Energy-efficient heating 

Because heat pumps rely on thermodynamics to transfer heat rather than generate heat, they require less energy compared to traditional heating and cooling systems. Heat pumps can produce three times more energy in heat form than the electricity input they consume.

Heat pumps can reduce the energy needed to heat a building by 65% compared to a gas furnace or baseboard heaters. They also consume less energy for cooling than air conditioners. Highly efficient heat pumps also provide better dehumidification than your standard air conditioners.

Heat pumps are also helpful in saving energy when heating water. Some heat pumps are fitted with a desuperheater, which captures waste heat from the system’s cooling mode. That heat can be used to supply hot water in your household. It's more efficient than using a regular electric water heater. 

Lower emissions 

Heating and cooling buildings contribute to 28% of global energy-related carbon emissions. Reducing carbon footprint is an urgent and important mission to which everyone must contribute. Changing how you heat your home or office is a great place to start.

Rather than relying on burning fuel to create heat, why not leverage the heat energy that's already present in the environment? Heat pumps have been grossly underestimated as a solution to lowering heating emissions. The International Energy Agency (IEA) estimates heat pumps could reduce global emissions by at least 500 million tonnes in 20301.

The heat pump must be embraced globally to reach its full potential in the fight against climate change. Also, we must increasingly shift to renewable energy sources of electricity like solar and wind power.

What to consider when choosing a heat pump system 

heat pump unit
Photo by Wikideas1 on Wikimedia Commons (Public Domain).

You'll have to do in-depth research into the types of heat pumps available to determine which one fits your needs. Consult a local HVAC technician to help you decide on which heat pump is ideal.

However, there are some general things to consider when choosing a heat pump.

Performance metrics 

Heat pump manufacturers typically rate the efficiency of the devices with a Seasonal energy efficiency rating (SEER) or a Heating seasonal performance factor (HSPF). High ratings indicate high efficiency.

The SEER is a ratio of how much heat (measured in BTUs) is discharged and the amount of electric Watts used in the cooling season. A SEER rating between 14 and 18 is excellent. HSPF, on the other hand, calculates the ratio of energy used during the heating season. An HSPF rating between 8 and 10 is great.

Prevailing climate 

Heat pumps work best in moderate climates. A heat pump's heat is milder than that provided by a furnace. However, it's quite difficult to benefit from heat pumps in colder climates where subfreezing temperatures remain for a long time.

However, the technology is developing relatively fast, and we expect cold-climate heat pumps to become common soon. Pairing the heat pump with other heating systems is the way to go. 

Costs

Besides the cost of purchasing a heat pump, there are other expenses to consider. You cannot install a heat pump yourself unless you are a certified HVAC technician. Hiring experts will cost you money.

Depending on the type of heat pump, you may need to integrate a backup heating option. Also, you'll need to spend some money on periodic checks of the heat pump system. Neglect will reduce the pump's efficiency and potentially erase the energy cost savings you hoped to get.

Conclusion

Heat pump systems transfer heat from various sources to where you need it to go. You can use it to bring cool or warm air into your house. Heat pumps use less energy than normal air conditioning or heating appliances. They are eco-friendly and can be run entirely on renewable energy.

Jen’s a passionate environmentalist and sustainability expert. With a science degree from Babcock University Jen loves applying her research skills to craft editorial that connects with our global changemaker and readership audiences centered around topics including zero waste, sustainability, climate change, and biodiversity.

Elsewhere Jen’s interests include the role that future technology and data have in helping us solve some of the planet’s biggest challenges.

Fact Checked By:
Isabela Sedano, BEng.

Photo by Wikideas1 on Wikimedia Commons (Public Domain).
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